PHASE-BEHAVIOR OF BINARY BLENDS OF SYMMETRICAL POLYSTYRENE-POLYBUTADIENE DIBLOCK COPOLYMERS STUDIED USING SANS

Binary blends of compositionally symmetric diblock copolymers are inve stigated using small-angle neutron scattering. The study focuses on th e miscibility of bleeds of polystyrene-polybutadiene diblock copolymer s as a function of chain length ratio and blend composition, and the r esults are related to the theoretical phase diagram put forward by M.W . Matsen (J. Chem. Phys. 103, 3268 (1995)). Three different low molar mass copolymers were blended with a high molar mass copolymer. We find very good coincidence with the theoretical phase diagram obtained. On ly for blends having a chain length ratio of 0.06, theory predicts tha t a larger amount of short copolymers can be dissolved in the matrix o f long copolymers, and vice versa. With the latter blends and volume f ractions of short chains between 0.11 and 0.70, the second-order Bragg -peaks do not vanish, which indicates that the lamellae are asymmetric .